1. Field of the Invention
The present invention relates to an image reading device that scans and reads a document, for use in a digital copier, an image scanner, and the like, and an image forming apparatus including the image reading device. In particular, the present invention relates to a sheet-through type image reading device including a document conveying device, which conveys a document and reads an image.
2. Description of Related Art
Conventionally, there is known an image reading device mounted on a multifunction peripheral or the like employing an electrophotographic process, which includes a document conveying device (automatic document feeder) which sequentially feeds sheet-shaped documents to a document placing table so as to read the documents and discharges the documents from the document placing table after finishing reading the documents. In such an image reading device, two kinds of reading systems may be employed, that is, a sheet-through system in which a document is automatically conveyed by the document conveying device and read with a document holder being closed, and a document fixing system in which the document holder is opened/closed for each reading so as to replace a document on the document placing table (contact glass) one by one, and an optical system (scanning means) is moved to read the document. Note that, according to the former sheet-through system, a reading operation of the document is performed under a state in which the optical system in the image reading device is held at a predetermined image reading position without being moved for scanning. On the other hand, according to the latter document fixing system, the reading operation is performed under a state in which the optical system therein is moved for scanning.
In an image reading device capable of performing reading with such a sheet-through system, conventionally, the document conveying device includes a conveyance guide which is disposed above the contact glass. Further, a reading guide is supported on the conveyance guide at a position facing an image reading region. After the document is guided along the conveyance guide, the document passes through a gap between the reading guide and the contact glass. After the document passes through the gap, the document is further guided to a downstream side by the conveyance guide. Then, the document is discharged to a document discharge tray.
FIG. 8 illustrates an example of a conventional conveyance guide and a conventional reading guide described above. FIG. 8 is a view illustrating a support state of a conventional first reading guide 83 with respect to a conventional first conveyance guide 81. As illustrated in FIG. 8, at an end portion of the first conveyance guide 81 on a front surface side (front side of FIG. 8) in a direction perpendicular to a document conveying direction (direction of the arrow illustrated in FIG. 8), a first support portion 81a is provided so as to protrude to the front surface side.
At an end portion of the first reading guide 83 on the front surface side, a first protruding portion 83a is provided so as to protrude to the front surface side below the first support portion 81a. In the first protruding portion 83a, an attachment screw 91 is allowed to pass therethrough upwardly from below in a slidable manner. A screw portion at a tip end of the attachment screw 91 is screwed into the first support portion 81a. 
A stop ring 93 is mounted to the attachment screw 91 at an upper side of a screw head with a predetermined gap therefrom. The first protruding portion 83a is slidable in an up-and-down direction between the screw head of the attachment screw 91 and the stop ring 93. Further, between the first support portion 81a and the first protruding portion 83a, a first coil spring 85 is disposed so as to surround a peripheral surface of the attachment screw 91. The first coil spring 85 biases the first protruding portion 83a in a direction separating from the first support portion 81a (lower side of FIG. 8).
With this structure, when the document conveying device (not shown) is opened or closed with respect to the contact glass (not shown), and accordingly the first reading guide 83 is separated from or brought into abutting contact with the contact glass (not shown), the first reading guide 83 moves in the up-and-down direction with respect to the first conveyance guide 81. Technologies described below are technologies for supporting the reading guide so that the reading guide is movable in the up-and-down direction with respect to the conveyance guide as described above.
For example, in a first related art, a reading guide member is supported by a main body (conveyance guide member) at two support portions on a front surface side and a back surface side, respectively. Specifically, the support portion on the back surface side supports the reading guide member so that the reading guide member is displaceable in an approaching/separating direction with respect to a contact glass, while causing the reading guide member to be biased toward the contact glass by a bias member. In addition, the support portion on the front surface side supports the reading guide member so that the reading guide member is displaceable in the approaching/separating direction with respect to the contact glass, within a smaller range than that of the support portion on the back surface side.
In the first related art described above, an attachment screw, which is allowed to pass through a through hole of the reading guide member upwardly from below, is screwed into a screw hole provided in the conveyance guide. In this manner, the reading guide member is supported by the conveyance guide member.
Further, in a second related art, a guide member (reading guide member) is disposed so that an upstream side thereof in a document conveying direction is swingable in the up-and-down direction, with a shaft, which is disposed in a support guide member (conveyance guide member) on a downstream side with respect to an image reading position, as a fulcrum. In addition, by a compression spring, the guide member is biased toward the contact glass with the above-mentioned shaft as a fulcrum.
In the second related art described above, an engaged pin, which is provided on the guide member so as to protrude axially outward therefrom, is inserted into a U-shaped engagement portion, which has both ends connected to the support guide member. In this manner, the guide member is supported by the support guide member on the upstream side of the above-mentioned shaft.
However, when the reading guide is supported by the conveyance guide with the use of the attachment screw as described in the first related art, the number of parts and assembly steps increase. Further, in a case where the pin formed in a horizontal direction slides in the up-and-down direction within the U-shaped engagement portion as described in the second related art, when the pin is disposed in an inclined state, the slidability in the up-and-down direction of the reading guide is reduced, and there is a risk of assembly failure. Further, in order to form the reading guide so as to be slidable in the up-and-down direction, other than the pin and the engagement portion, a swing pivot is also required to be formed.